The present invention relates to a method of monitoring an immunoassay test, in particular to monitoring the quality of an immunoassay test while the test is being carried out. This makes it possible for a user to, if necessary, adjust one or more parameters of the test while it is being run to improve the conditions under which the test is run.
As is known, an immunoassay test may be used to detect the presence of particular compounds, such as drugs, in the body. Known methods of testing include immunoassay “strip” testing where an antibody is labelled with a visible marker, and is drawn along a membrane passing over test zones (or “active zones”) and a control zone impregnated with analyte conjugate substances or other binding substances. The presence of particular compounds in the sample are detected by a visible change occurring the in the corresponding zone of the strip owing to the interaction of the labelled antibodies and the conjugate substances resulting in visible lines forming on the strip in some of the zones. The colour formed may, depending on the assay format, be proportional or inversely proportional to analyte concentration in the fluid sample.
In one such test a sample of bodily fluid, such as blood, sweat, urine or saliva, is placed at an upstream end of an immunoassay region, which is normally in the form of a strip, and is drawn along the strip by capillary action. One zone of the strip, at or near the upstream end of the strip, contains an antibody for a particular drug labelled (conjugated) with a suitable marker. When the sample of bodily fluid passes through this zones, the particular drug will, if it is present in the sample of bodily fluid, bind with the antibody. The strip further comprises one or more active zones which contain a drug-protein derivative specific to the drug that is being tested for. When the sample of bodily fluid passes over the active zones, because the antibody-marker conjugate has already bound to the drug in the sample, it is not free to bind with the drug-protein derivative bonded on the target region of the strip. However, if the particular drug is absent from the sample of bodily fluid, the antibody-marker conjugate will be free to bind with the drug-protein conjugate in the active zones, causing the antibody-marker conjugate to become immobilised at the site of the drug-protein conjugate in the active zones. As a result, a visible marker is deposited in the active zones, as a coloured line or stripe.
In practice, a typical immunoassay strip will include a number of active zones, each containing a drug-protein derivative specific to a respective drug to allow more than one drug to be tested for.
A typical immunoassay strip further includes a control region at or near its downstream end. When the sample of bodily fluid reaches the control region a known reaction leading to a visible indication, for example a colour change, occurs. When the visible indication occurs in the control zone, this indicates that the sample of fluid has passed along the length of the strip to the control zone and that the test has been successfully run. The visible indication in the control zone may also be used in calibrating the results obtained in the various active zones of the strip.
The active zones and control zones are normally separated by background zones that contain no drug-protein conjugate.
The part of the strip extending from the region on which the fluid sample is placed to the control zone constitutes the “active area of the strip”. An end pad may be placed downstream of the active region to absorb any fluid that reaches the downstream end of the active region.
Immunoassay tests of this nature are well-known. Mobile screening devices that can perform such an immunoassay test are also known, for example for use at the roadside, in a sporting stadium etc. In general, mobile devices comprise some form of reader, into which is inserted an immunoassay cartridge. The immunoassay cartridge consists, in general, of an immunoassay strip contained in a suitable housing. A sample of bodily fluid may be placed on one end of the immunoassay strip, by means of an entry port provided in the housing of the cartridge.
One example of an immunoassay reader is disclosed in WO 00/04381. A fuller description of the immunoassay process is contained therein.
A first aspect of the present invention provides a method of monitoring the quality of an immunoassay, the method comprising determining the position of the flow edge of fluid across an immunoassay region;                determining a value of a parameter representing variation with time of the position of the flow edge of fluid across the immunoassay region; and        obtaining information about the quality of the immunoassay from the value of the parameter.        
In a conventional method of performing an immunoassay, the test fluid is required to traverse the entire length of the immunoassay strip before the strip is examined to determine whether physical markers have been deposited in any of the active regions. It takes a finite time for fluid to traverse along the length of the active area of the strip; in fact, it is normal to leave the strip for a time of period, known as the “incubation time”, after the fluid has travelled the length of the strip to the control zone. Thus, the strip is not normally examined before a time equal to the incubation time plus the time required for fluid to travel along the length of the active area of the strip has lapsed. A normal time for fluid flow from initial detection to reaching the end pad might be tens of seconds or so, and a total incubation might be a couple of minutes. If, as an example, the police are carrying out a roadside check on a driver, the driver is unavoidably detained for at least this time, even if the results of the test eventually indicate that the driver is in a legally fit state to drive. Moreover, if the test should not work satisfactorily, this is not known until the end of the incubation period.